1. Field of the Invention
The present invention relates to a DVD seamless playback system, and more particularly, to a DVD seamless playback system having two alternatively set timers.
2. Description of the Prior Art
DVD-Video was originally designed to meet the requirements of the movie industry, in particular, to provide a complete movie on a single “compact” optical disc. In the 1990s, several technology companies, such as Pioneer, Sony and Philips, started to develop a new digital video disc format, with the goal of recording two or more hours of high-quality video onto one disc, as a next-generation replacement for the LaserDisc (LD). In the end of 1995, Pioneer launched a digital versatile disc, called for short the DVD, a totally new type of optical storage media for storing video data. From then on, DVD become one of the most popular video storage media. The first DVD-Video player for playing video stored in a DVD went on sale shortly thereafter.
Since DVD was intended as a technology to replace LaserDisc (LD), DVD needed to provide at least equivalent video quality. As the result of many rounds of video quality evaluation, and with the assumption that DVD would use variable-rate video compression, it was determined that a data rate of 3.5 Mbps was the minimum requirement. Then, considering audio quality, flexibility for international use, and multimedia capability, it was decided to provide capacity for Dolby AC-3 audio in three languages (384 kbps×3) and subtitles in four languages (10 kbps×4), resulting in the design of a specification which required a disc capacity of 4.7 GB. A DVD therefore has playback time of about 133 minutes, which is long enough to allow most movies to fit onto a single disc.
DVD is designed to achieve a disc capacity of 4.7 GB, based on the evolution in technology in the ten-plus years since the CD was introduced in 1982. The difference between the DVD specification and the CD specification is not just the move from a near-infrared laser to a red laser. For example, the standard CD track pitch is 1.6 microns, and reducing this by the ratio of DVD to CD laser wavelength (650/780) would result in a 1.33 micron track pitch. However, DVD actually requires a track pitch of 0.74 microns, meaning that tracks are considerably more packed than one might expect. As the track pitch decreases, crosstalk increases, and the radial tilt margin is severely reduced. To be precise, DVD had to be designed with sophisticated skill to guarantee that the quality of data stored in a DVD attained a satisfactory standard.
The files used for DVD-Video and DVD-Audio are arranged in directories called VIDEO_TS and AUDIO_TS respectively. The files in these directories have predetermined names and extensions. Files with the extension “.IFO” contain application information needed to reproduce the content. Files with the “.VOB” extension contain the actual video or audio content.
DVD-Video contains not only the actual video and audio content, which are called “presentation data”, but a variety of powerful information which enables features peculiar to the DVD format, such as multi-angle viewing, parental lock, random shuffle playback, etc., and also provides support for special playback modes such as fast forward and reverse. These special extra information are called “navigation data”. The navigation data is in essence used to control the presentation of the presentation data.
The navigation data is composed of video manager information (VMGI), video title set information (VTSI), program chain information (PGCI), presentation control information (PCI), and data search information (DSI). In addition to the video and audio content, as described above, the presentation data further consists of sub-pictures. The presentation data consists of at least a title, each of the titles consisting of at least a program chain (PGC). A first program chain in a title consisting of a plurality of program chains is called an Entry PGC. A program chain is composed of a program chain consisting of a precommand, a posecommand and cells, and a plurality of cells in a video object (VOB).
As mentioned above, since DVD requires well thought out solutions to guarantee that the quality of data stored in a DVD attain a satisfactory standard, how to implement these solutions is becoming one of the most important issues in the DVD industry.